The invention relates to a manual control device in accordance with the preamble of claim 1.
Such a manual control device is known from the publication of a German company "Kleinmeisterschalter MO . . . nach Ma.beta.blatt M7221, Spohn+Burkhardt, Januar 1991" [Small Master Switches MO . . . in Accordance with Specification Sheet M 7221].
Manual control devices operating in a stepped manner, such as those known from this publication, are equipped with switch elements which are switched on or off as a function of the position of the control stick and by means of that result in the desired stepped characteristic of the control voltage.
Thus, such manual control devices have as a function of the number of steps a relatively large number of on-off switches, for example microswitches, which are actuated by the manual control device on its deflection path. This requires a high manufacturing outlay because of the plurality of error-prone switching elements, which furthermore require a relatively large space and in this way can negatively affect the structural shape of the manual control element.
On the other hand, in connection with many exemplary embodiments, depending on the object to be controlled, such as a crane or other construction apparatus, it is necessary to have discrete voltage values available as control input values for these devices, so that it is not easily possible to do without an appropriate stepping of the control signal for the machine to be controlled.
A manual control device with a control stick is known from DE39 11 171A1, whose angular deflection is converted into a proportional control signal which is interrupted by plateau-like intermediate areas, wherein electronic means are provided by means of which this characteristic of the output signal can be adjusted. These plateau-like intermediate areas are used to eliminate inaccuracies in the positioning of the control stick because of mechanical tolerances, but they do not change the basically proportional switching behavior of this known manual control device to the extent that between these plateaus the control signal extends proportionally with the deflection of the control stick. A stepped characteristic of the control voltage cannot be represented by means of this manual control device, which essentially generates a control signal proportional to the control stick deflection.
U.S. Pat. No. 5,134,395 discloses an interface for the connection of control sticks (joysticks) and switches to the connector Rs232 of a PC, for which purpose an analog-digital converter in particular is employed. As cannot be expected otherwise with an analog/digital conversion, the result of this circuit is that the analog joystick signal is digitized and in this way made available to the downstream connected PC. As with every digitalization, the digitalization necessary for a connection to a PC also causes the conversion of the analog signal of the joystick into an extremely finely "stepped" output signal, whose number of steps inevitably corresponds to the selected resolution or the number of available bits; with the customary 8-bit conversion, the full deflection of the joystick is therefore converted into "bit steps". A pure digitalization is not suitable for the generation of discrete voltage values.
EP-A-0 495 280 also refers to the digitalization of an analog signal for generating a signal in a control circuit which is intended to be used for the compensation of drift appearances of the input signal. If defined permissible values are exceeded, a microcontroller causes a step-like retardation of the dc pre-voltage of a measurement value amplifier. A connection with manual control devices cannot be found in this known complex circuit arrangement.